This invention relates to retrievable bridge plugs for use in sealing a casing in a well, and more particularly to such plugs of the type using an elastomeric packer to effect sealing.
The bridge plug of the present invention is of the type having upper and lower anchors with the elastomeric packer positioned about a mandrel therebetween. Drill string manipulation is used to set the anchors and compress the packer thus sealing the casing at a selected location.
Such plugs, when so set, can be subject to large hydraulic pressures from either below or above the plug. Even slight slippage of the anchors against the well casing can cause a reduction of the packer-compressing force and the seal formed by the packer may be lost.
In the past, plugs have been provided with means for maintaining packer-compression force independent of that provided by the anchors. Such past plugs include ratchet mechanisms which are actuated by drill string manipulation and when so actuated, maintain the packer in a compressed condition.
One such past ratchet mechanism is formed on facing radially inward and outward surfaces. Each ratchet surface is helically formed, in the manner of a screw thread. Disengaging the ratchet mechanism requires rotation of the drill string to unscrew it. Such rotation requires a tremendous amount of torque in view of the force required to properly set the packer. Another past mechanism uses a ratchet to maintain packer compression and a system of shear pins and retaining rings to relieve packer-deforming pressure as well as release the anchors. This permits only one setting of the plug, since if it is desired to reset the plug, it must be withdrawn and the rings reset with new shear pins.
It is an object of the present invention to provide a retrievable bridge plug which overcomes the above-mentioned problems which exist in past plugs.
It is a more specific object of the invention to provide a retrievable bridge plug in which an elastomeric packer can be set or released in response to longitudinal movement of the plug body.
The instant embodiment of the invention includes a center mandrel having a packer mandrel concentrically mounted thereover. A packer carried about the packer mandrel, is compressed responsive to downward movement of the packer mandrel. Cooperating ratchet surfaces are provided about a portion of the packer mandrel and on the radially inward faces of collar segments which are fixedly disposed about the mandrel. A tang on the radial inward face of each collar segment extends through a longitudinal slot in the packer mandrel and contacts the center mandrel. The collar segments are all radially biased inwardly and each tang abuts against the center mandrel. A cam surface on the center mandrel causes radial inward and outward movement of the segments, dependent upon longitudinal center mandrel position, thus engaging and disengaging the ratchet surfaces. When engaged, the ratchet action between the two surfaces permits movement of the packer mandrel only in a packer-compressing direction.
These and other attendant objects and advantages of the invention will become more apparent in view of the drawings and following detailed description of the invention.